<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <meta  name="description" content="使用transition可以创建简单的过渡动画，适用于鼠标悬停、焦点等触发的状态变化">
    <style>
        .content{
            height: 100px;
            width: 100px;
            background: red;
            border-radius: 50%;
            box-shadow: 0 0 0 10px blue,
                        0 0 0 20px green,   /**使用box-shadow模拟边框 */;
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%,-50%);                    
            transition: box-shadow 1s ease-in-out;
        }

        .content:hover{
            box-shadow: 0 0 0 10px blue,
                        0 0 0 20px green,
                        0 0 0 30px yellow;
        }


    </style>
    </style>
</head>
<body>
    <div class="content"></div>
</body>
</html>